FOUS30 KWBC 230746
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
346 AM EDT Thu Apr 23 2026

Day 1
Valid 12Z Thu Apr 23 2026 - 12Z Fri Apr 24 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN THE CENTRAL
PLAINS AND UPPER MIDWEST...

Convection is expected to blossom this afternoon along and ahead of
a cold front in the Central U.S. The warm sector ahead of the front
should be characterized by an overlap of moderate instability (1000
to 2000 j/kg MLCAPE) and anomalously high moisture content (1.0 to
1.5 inch PWATs; near or above the 90th percentile for late April).
The combination of instability and moisture should support heavy
rain rates in organized convection in excess of 1 inch per hour at
times. The main limiting factor for higher rainfall totals over the
entire forecast period, and any impacts from flash flooding, should
be a lack of persistence to the high rain rates in a given spot.

From the I-70 corridor to the north, lines of thunderstorms are
expected to be relatively narrow and steadily progress, given the
deep layer shear vectors will be oriented closer to perpendicular
with the cold front. Therefore, despite some pockets of lower flash
flood guidance (around or just under 2 inches in 3 hours), and
recent wet pattern in parts of the region, the heaviest rain rates
should not last very long and the flash flood risk is expected to
remain isolated. Furthermore, instability diminishes rapidly around
sunset, so rain intensity should drop off within about 6 hours of
convective initiation. It should be noted this assessment does not
necessarily apply to other flooding risks in the region: ongoing
mainstem river flooding, or potential for rain and snowmelt
flooding in the Upper Peninsula of Michigan. For more details on
those flooding hazards, refer to the National Water Center.

Further south, the pattern will be more supportive of backbuilding
and training convection, especially this evening and overnight from
southeast Kansas into northeast Oklahoma and the Ozark region of
southwest Missouri and northwest Arkansas. As the low level jet
veers and an upstream instability maximum persists in eastern
Oklahoma, hi-res models uniformly show a band of thunderstorms
becoming increasingly east-west oriented, more parallel to the deep
layer shear vector. Nevertheless, they all also show steady
progression to the southeast with some cold pool development, and a
lack of rainfall maxima in excess of 3 inches. Therefore, the risk
of flash flooding is currently expected to be isolated, but the
situation will be monitored in case a targeted Slight Risk is
needed later today.

Lamers


Day 2
Valid 12Z Fri Apr 24 2026 - 12Z Sat Apr 25 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN THE MID SOUTH...

A convective cluster or backbuilding convective line may be ongoing
on Friday morning -- most likely across northern Arkansas based on
00Z HREF EAS probabilities -- with the potential for additional
convective clusters to develop through the day across the region.
Updated WPC QPF places the heaviest rainfall across Arkansas,
northern Mississippi, and far northern Louisiana, and this is where
the Marginal Risk area was re-centered. There is some uncertainty
on where the heaviest rain will fall, as it should be tied in some
way to convective outflow from morning and early afternoon
activity. The warm sector to the south and southeast of that should
have a combination of moderate instability and precipitable water
close to 1.5 inches (around the 90th percentile for late April).
That sort of environment would support rain rates of 1 to 2 inches
per hour in organized convection, which could lead to isolated
flash flooding where backbuilding and training occurs.

Lamers


Day 3
Valid 12Z Sat Apr 25 2026 - 12Z Sun Apr 26 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL IN SOUTHEAST
KANSAS, SOUTHWEST MISSOURI, EASTERN OKLAHOMA, AND WESTERN ARKANSAS...

Available deep moisture in the southern Plains on Saturday should
be lower than prior days across the region, with model forecast
soundings indicating the potential for dry air from 800-600mb
associated with an elevated mixed layer. This would likely restrict
any excessive rainfall and flash flooding concerns to the isolated
variety. Nevertheless, strong instability and vertical wind shear
should support supercells evolving into convective lines. There is
not a consistent signal for concentrated areas of heavy rain, but
with the expected convective modes, localized areas of longer heavy
rain duration are possible via storm mergers and some upshear cell
development. Any corridors of heavy rain on Thursday or Friday
could also locally increase soil moisture and vulnerability to
another round of heavy rain. Therefore, the Marginal Risk was
maintained for Saturday and Saturday Night.

Lamers
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